Hydraulic brake system with slip control

ABSTRACT

The present invention relates to a slip-controlled brake system including digitally controlled electromagnetic inlet valves and outlet valves, and the inlet valve has a restrictor valve control responsive to differential pressures in order to minimize valve noises.

TECHNICAL FIELD

The present invention relates to hydraulic brake systems with slipcontrol, and more particularly relates to hydraulic brake systems withslip control wherein the discontinuous pressure fluid control in theslip-controlled brake systems causes an undesirable sound emission dueto the pulse-type pressure variation.

BACKGROUND OF THE INVENTION

It has been found in the brake system described in patent applicationSer. No. 43 19 227 (not published) that the proposed constructivesolutions with respect to the arrangement of the annular pistonincluding a controllable restrictor and the details in the solenoidinlet valve, which correspond to the annular piston, require furtherstructural simplification to achieve a most simple miniaturized inletvalve design.

A solenoid valve is disclosed in European patent application No. 0 317305 which is suitable for use in anti-lock hydraulic brake systems. Thesolenoid valve has a magnetic core accommodating a coil. The magneticcore is confined by a magnetic armature on one side and by a restrictormember on the other side. The restrictor member has a passage which isclosable by a valve needle. The restrictor member is compressed in anaxially movable fashion between the magnetic core and a housing cover,in which the pressure fluid inlet is provided, so that in the switchingposition, where the valve needle closes off the supply duct in therestrictor member, a differential pressure acts on either side of therestrictor member and causes a displacement of the valve needle inrelation to the magnetic armature. A compression spring interposedbetween the valve needle and the magnetic armature is preloaded thereby.The preloading force of the compression spring caused by the differencein pressure on the restrictor member results in a quick release of themagnetic armature from the magnetic core when the electromagneticexcitation is interrupted. This results in short valve opening times. Aspring resetting force acting on the valve needle in the opening sensefavors the quick opening of the supply duct in the restrictor member.Thus, pressure fluid propagates to an annular slot after having passedthrough the free passage at the valve needle. The annular slot isprovided between the hollow-cylindrical inside wall of the magnetic coreand the outside wall of a cylindrical part guiding the valve needle. Thefluid which emanates from the valve inlet is conducted through thesupply duct in the restrictor member and the subsequent annular slotinto a pressure fluid connection which leads to the pressure fluidconsumer.

While the circuit configuration of the brake system disclosed in themain application remains unmodified, an object of the present inventionis to suggest solutions for miniaturizing the inlet valve which can beachieved at low cost without limiting the operability of the valve.

According to the present invention, this object is achieved by theannular piston, which accommodates the controllable restrictor, which isaxially movable within an annular chamber in the valve carrierconcentrically relative to the valve closure member of the inlet valve.

Thus, the annular chamber, which originally accommodates an annularfilter and the valve closure member, additionally serves for thefavorable integration of the annular piston, thereby permitting theexternal dimensions of the valve carrier and the dimensions of thestepped bore of the valve accommodating member to be maintained.Further, the annular portion between the valve accommodating member andthe valve carrier can be used to position the annular filter. Afavorable increase of the filter surface for filtering the fluid which,among others, flows between the wheel brake and the non-return cup sealis thereby achieved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial view of an inlet valve on an enlarged scale,including the arrangement of the annular piston according to the presentinvention proximate the valve closure member.

FIG. 1A is a schematic depiction of a hydraulic circuit whichincorporates the inlet valve of the present invention.

FIG. 2 is a second embodiment of the present invention.

FIG. 3 is a cross-section view taken along the line of intersection A--Aof the valve carrier on an enlarged scale.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIGS. 1 and 1A show a constructive embodiment of the present inventionwith respect to the overall structure of an inlet valve 1. Inlet valve 1comprises a valve carrier 10 which includes a valve closure member 11and the ducting of a main pressure line 2 emanating from a brakingpressure generator 5 and an auxiliary pressure pump 18. Valve carrier 10is preferably integrated in a valve accommodating member 9 in acartridge-type construction (as a screw-in cartridge, staked cartridge,cartridge with spreading ring). In the chosen illustration of the valveattachment system, the valve carrier 10 in the conically tapered outsideportion is secured with a spreading ring 128 in the valve accommodatingmember 9. The opening in the valve accommodating member 9 has a conicalundercut to receive the spreading ring 128. The valve carrier 10 issealed in the valve accommodating member 9 by a seal which is arrangedbelow the conically shaped valve carrier 10.

There is a pressure fluid connection (line 16,20) between the mainpressure line 2, which is connected to the braking pressure generator 5and the auxiliary pressure pump 18, and the annular piston 8 by way of aplate filter 21, which is snapped onto the extension of the valvecarrier 10 and the normally open valve closure member 11. Line 16 alsois in hydraulic communication with pressure fluid collection means 19and outlet valve 17. Pressure fluid propagates from the annular piston 8towards the annular filter 22, which is connected upstream of theconnection to the wheel brake 3, through the open annular slot at amagnetic core 127 and also, to a small extent, through a restrictor 4 toan invariable orifice 31 machined in the valve carrier 10. Theinvariable orifice 31 is used to improve the ABS control quality.

A transverse bore in its wall permits the annular piston 8 to performthe controllable restrictor function. In an annular chamber 126, theannular piston 8 is axially movable on the extension of the rotationallysymmetrical central element 114 including a valve seat 116, theextension being reduced in diameter. By the action of a compressionspring 7, the annular piston 8 is supported with its external collar119, acting as a stop, on the bore step of the annular chamber 126 inthe valve carrier 10. Substantially, the annular piston 8 takes theshape of a sleeve which, at its front surface close to the magnetic core127, has a funnel-shaped rubber sealing seat 115 which is opposed to theconical frontal end of the magnetic core 127. Upon request orrequirement, the conical sealing can also be provided by a metallic flatseal or an O-ring embedded in the front surface area of the annularpiston 8.

A sealing ring 124 is provided on the frontal end of the annular piston8 remote from the magnetic core 127. Sealing ring 124 prevents an escapeflow of pressure fluid from the braking pressure generator 5 in thedirection of the wheel brake 3 in the closed condition of the inletvalve 1. The rotationally symmetric central element 114, which projectswith its extension into the interior, is press fitted in the steppedbore of the valve carrier 10 and, if necessary, staked in the frontalend area. In the embodiment shown, the valve seat 116 is a steppedsleeve part and is press fitted in the bore of the central element 114which extends coaxially relative to the valve closure member 11.

An annular groove, which is positioned on the outside periphery of thevalve carrier 10 at the level of the central element 114, accommodates asealing cup 112 which shuts off fluid flow in the direction of the wheelbrake 3. The sealing cup 112 permits a pressure fluid connection,filtering the fluid, between the wheel brake 3 and the braking pressuregenerator 5 or the auxiliary pressure pump 18. The pressure fluidconnection is established by way of an annular filter 22, spaced betweenthe valve carrier 10 and the valve accommodating member 9, and at leastone lateral recess 120 at the plate filter 21, which can be seen in thedrawing.

In contrast to the embodiment of FIG. 1, FIG. 2 shows (also on aconsiderably enlarged scale) the valve seat 116 integrated as ahomogeneous component in the central element 114. This obviates the needfor the separate arrangement of another sleeve-shaped press-in partincluding the valve seat 116, as explained in the embodiment of FIG. 1.To pressurize the sealing ring 124 provided on the annular piston 8, thecentral element 114 has only one aperture 118 that is dimensionedcorrespondingly large and permits low-cost manufacture as a bore. Toexactly adjust the quantity of fluid flow to the wheel brake 3 duringABS control operations, an invariable orifice 31 in the valve carrier 10is additionally press fitted as an insert member in the transverse bore13 of the valve carrier 10. Transverse bore 13 hydraulically connectsthe annular chamber 126 to the wheel brake 3. If necessary, the functionof the invariable orifice is possible also by a calibrated fine boringof the transverse bore, as shown in the embodiment of FIG. 1. The valvecarrier 10 is retained by a self-shearing attachment in the valveaccommodating member 9, so that the sealing ring known from FIG. 1 canbe eliminated.

All other elements, which can be seen in the illustration of theembodiment of FIG. 2, are substantially identical with the design andfunction in FIG. 1.

FIG. 3 shows a top view of the inlet valve 1 shown in FIGS. 1 and 1A,taken along the line of intersection A--A. The view shows that thecentral element 114, because of its square-section design, providescorrespondingly large pressure fluid passages with respect to the insidewall of the valve carrier 10 in the direction of the sealing ring 124which precedes the annular piston 8. The cross-sectional plane extendsthrough the bottom end portion of the valve carrier 10 onto which theplate filter 21 is snapped. Spread over the periphery of the platefilter 21 are several recesses 120 which provide a pressure fluidpassage from the direction of the sealing cup 112. Thus, all elementsdescribed with respect to the cross-sectional plane A--A have arotationally symmetrical coaxial arrangement relative to each other.

The operation of the present invention will be explained in thefollowing.

During an uncontrolled slip-free normal braking mode, the inlet valve 1adopts its electromagnetically non-excited open initial position. Whenthe braking pressure generator 5 is operated, pressure will notaccumulate at the inlet of the inlet valve 1 because the valve seat 116has no considerable throttling or restricting effect. A considerabledifference in pressure between the valve inlet and valve outlet isthereby prevented. The annular piston 8 remains in abutment on the borestep in the initial position shown in the drawing, so that brakingpressure can be applied to the wheel brake 3 by way of the valve seat116 and the annular slot between the annular piston 8 and the magneticcore 127.

When the brake pedal is released, the braking pressure decreases againin the opposite direction towards the braking pressure generator 5 byway of the open valve closure member 11 and the sealing cup 112.

When the inlet valve 1 is closed and the difference in pressure betweenthe valve inlet (master cylinder pressure/pump pressure) and the valveoutlet (wheel braking pressure) exceeds a value adjusted by thecompression spring 7 during a brake slip control operation, theresultant pressure force on the sealing ring 124 causes the annularpiston 8 to displace in opposition to the spring force and to move intosealing abutment on the magnetic core 127. Thus, there is a pressurefluid connection to the wheel brake 3 exclusively by way of therestrictor 4 of the annular piston 8. When the inlet valve 1 reopens itsregular passage by way of the valve closure member 11, the fluidreplenished by the auxiliary pressure pump 18 in operation propagates tothe wheel brake exclusively by way of the restrictor 4 in the annularpiston 8 and is slowed down such that the pressure surge and, thus, thenoise is reduced during subsequent repeated closing operations of theinlet valve 1. When the switching pressure differential necessary forthe actuation of the annular piston 8 falls short of and the brakingoperation is interrupted, the annular piston 8 returns to its initialposition where the passage cross-section is increased.

I claim:
 1. Hydraulic brake system with slip control, of the typeincludinga braking pressure generator which is hydraulically connectedto at least one wheel brake by way of a main pressure line, a returnline connected to said at least one wheel brake and to a pressure fluidcollecting means, an auxiliary pressure pump having an auxiliarypressure line hydraulically connected to the braking pressure generator,inlet valves and outlet valves inserted in the main pressure line andthe return line, a controllable restrictor inserted in the main pressureline between the inlet valve and the wheel brake which establishes anunimpeded hydraulic fluid passage in the main pressure line to said atleast one wheel brake in a first switched position and limits thepressure fluid passage to the wheel brake in another switched position,comprising:a valve accommodating member; a valve carrier being receivedin said valve accommodating member and having an annular chambertherein; an annular piston being received in said annular chamber ofsaid valve carrier and being axially movable relative to said chamber,wherein said annular piston accommodates said controllable restrictor;and a closure member for said inlet valve also being received withinsaid valve carrier.
 2. Hydraulic brake system as claimed in claim 1,wherein the annular chamber includes a stepped bore which is confined bya magnetic core of the inlet valve on a first frontal end of saidmagnetic core and by a central element accommodating a valve seat on asecond frontal end.
 3. Hydraulic brake system as claimed in claim 2,wherein a front surface of the annular piston proximate to the magneticcore has a sealing seat that is movable into abutment on a frontal endof the magnetic core.
 4. Hydraulic brake system as claimed in claim 2,wherein the annular piston has a collar which is positioned on thestepped bore of the annular chamber and supported on a compressionspring mounted on the magnetic core.
 5. Hydraulic brake system asclaimed in claim 1, wherein the annular piston is guided between acentral element including a valve seat and a wall of the annularchamber.
 6. Hydraulic brake system as claimed in claim 5, wherein anintermediate space to accomodate a sealing ring is provided between afront surface of the central element and a front surface of the annularpiston proximate to the central element.
 7. Hydraulic brake system asclaimed in claim 6, wherein the central element has at least oneaperture having an axis in the direction of its axis of symmetry whichestablishes a permanent pressure fluid connection between the mainpressure line extending from the direction of the braking pressuregenerator and the intermediate space accommodating the sealing ring. 8.Hydraulic brake system as claimed in claim 1, wherein said closuremember is received in said annular chamber of said valve carrier forselective contact with a valve seat.
 9. Hydraulic brake system asclaimed in claim 1, wherein said controllable restrictor is a borelocated in said annular piston.